Add basic SPI support and associated documentation.
v2: remove baud rate check, fix baud rate calculations
v3: finish transaction with BSY check, disable SPI when not in use
Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>
Add a fully functional STM32F1 port, currently mostly targeting STM32F103
microcontrollers. This requires an 8 MHz XTAL. The maximum possible step rate
is around 282K steps per second.
This uses stm32flash to burn the firmware. The bootloader needs to be started
by setting BOOT0 to 1 and resetting the MCU. There is no automatic bootloader,
unlike on Arduino.
Signed-off-by: Grigori Goronzy <greg@kinoho.net>
